The present invention pertains to method and apparatus for mechanically propelling game balls to simulate the action of such a ball when stroked with a hand held implement, such as occurs in stroking a tennis ball with a tennis racket.
The use of mechanical methods and devices for automatically throwing or propelling tennis balls for practice and in the training of students and players of tennis is in general known. For example, machines are available which may be positioned on one side of a tennis court for sequentially ejecting a series of tennis balls carried in a refillable hopper, in which the trajectory of each propelled ball passes over the tennis net onto the opposing side of the court where an awaiting player practices his return stroke in response to the artificially delivered ball. The trajectory of the balls can be selected and is, of course, repetitive, allowing the player to concentrate on particular return strokes.
Although it is thus seen that devices of this type have an established utility, the available mechanisms are relatively large and bulky and thus are not readily portable in the sense that they can be hand carried by a single person onto a tennis court. Moreover, the devices are expensive, beyond the financial resources of many tennis instructors, and beyond the pocket book of most recreational and amatuer tennis students and players. Additionally, because of the mechanical operating characteristics of these known devices, they are typically subject to substantial mechanical vibration and component wear resulting in a shortened useful life and frequent breakdown of the apparatus. Many of these devices also require electrical power for their operation, thus limiting their usefulness inasmuch as many tennis courts do not have the necessary electrical facility. Other devices, again because of their mechanical operating characteristics, are powered by small gasoline engines which emit dangerous exhaust fumes precluding their use on indoor courts.
Another disadvantage of many existing tennis ball throwing mechanisms is their inability to realistically simulate the action of a racket stroked tennis ball. For ground strokes, which is the most frequently used stroke during a tennis game, the ball is usually struck by the racket in a manner which imparts either a top spin or a bottom spin to the propelled ball. Most often, a top spin is delivered to the ball to cause it to drop more quickly on the opposing court for controlled placement. Although devices having the ability to impart spin to the tennis ball are, in general, known, such devices are either unable to realistically simulate a ball spin developed by a tennis racket or lack some other important, desirable feature such as reasonable price, reliability or portablility, simplicity of operation, and adjustability in speed of ball delivery and ball spin.